Seasonal Climate Outlook Message for May to August 2004

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Recent Rain Welcome 05/04/04

Recent rain over much Queensland was welcome by many producers but has created a few headaches for those still harvesting crops especially cotton. Moderate falls of between 10-80mm were recorded over many areas of Queensland with a few locations receiving over 100mm.

This rainfall coincided with the latest passage of the MJO (also know as the 40 day wave). There are some indications that the MJO may continue to have an influence on our weather through to the second week of May.

The MJO is simply a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events across much of Queensland. If it's timing remains current it would next be expected to have an influence on our weather around mid June.

With the longer term outlook, the SOI has remained in negative values with the 30day average of the SOI as of the 3rd May being minus 10.3.

Based on the SOI pattern over March and April, rainfall probabilities are relatively mediocre (less than 50% chance of getting above median rainfall through to the end of July) across most of Australia. The lowest rainfall probabilities (10-30%) can be found in central and southern NSW, most of Victoria, south east and north east WA, south west SA, and across most of the NT.

There is a more reasonable 50-70% chance of getting above median rainfall through to the end of July for the south east corner of the Queensland as well as for parts of the north Queensland tropical coast.

As rainfall probabilities and median rainfall levels vary between locations we recommend referring to Australian Rainman for specific rainfall data.

In the short term the fall in value of the SOI does not pose an immediate problem. However if this trend continues it could be a concern in the longer-term. For example if the SOI were to remain in a 'consistently negative' pattern through to the end of May, rainfall probabilities across Queensland for the following 3 months would drop further.

For more information try www.longpaddock.qld.gov.au http://www.longpaddock.qld.gov.au> or www.dpi.qld.gov.au/climate http://www.dpi.qld.gov.au/climate> Otherwise feel free to give me a call through the DPI call Centre on 13 25 23.

The full story

SOI in "Falling Phase" 05/04/04

The SOI has remained in negative values with the April monthly average of the SOI being minus 16.2. Based on the pattern of the SOI over March and April, there is a mediocre 30-50% chance of getting above median rainfall through to the end of July across most of inland Queensland.

There is though, a more reasonable 50-70% chance of getting above median rainfall through to the end of July for the south east corner of the state as well as for parts of the north tropical coast.

While the fall in value of the SOI does not pose an immediate problem, if this trend continues it could be a concern in the longer-term. For example if the SOI were to remain in a 'consistently negative' pattern through to the end of May, rainfall probabilities across Queensland for the following 3 months would drop further. A 'consistently negative SOI phase' at the end of May would also increase the chance of an earlier average start and later average finish to the severe frost season in many locations. Therefore we continue to recommend keeping an eye on the SOI trends.

When using probabilities or a percentage chance of something occurring, it is important to consider the opposite view. For example, currently Yuleba has a 35% chance of getting at least its long term May to July median rainfall of 95mm. This also means that there is a 65% chance of not getting at least 95mm.

Another way of looking at this is that in 3 to 4 years out of 10 (or around one third of years) with the current SOI pattern, Yuleba has received at least 95mm for May to July. Therefore in 6 to 7 years out of 10 (or two thirds), Yuleba has gotten less than 95mm for this period.

Rainfall probabilities are also fairly mediocre (less than 50% chance of getting above median rainfall through to the end of July) across the rest of Australia. The lowest rainfall probabilities (10-30%) can be found in central and southern NSW, most of Victoria, south east and north east WA, south west SA, and across most of the NT.

As rainfall probabilities and median rainfall levels vary between locations we recommend referring to Australian Rainman for specific rainfall data.

Many people like to follow the relationship between the SOI and rainfall patterns in more detail for their area. Finding out what conditions where like in your area for May to July in 1997, 1995, 1994, 1993, 1976, 1969, 1967, 1965 and 1952 and comparing it to your 'normal' rainfall for May to July could be useful.

Recent rain (late May early April) over much Queensland was welcome by many producers but has created a few headaches for those still harvesting crops especially cotton. Moderate falls of between 10-80mm were recorded over many areas of Queensland with a few locations receiving over 100mm. This rainfall coincided with the latest passage of the MJO (also know as the 40 day wave). There are some indications that the MJO may continue to have an influence on our weather through to the second week of May.

The MJO is simply a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events across much of Queensland. If it's timing remains current it would next be expected to have an influence on our weather around mid June.

According to the Bureau of Meteorology's "El Nino Wrap Up" the current El Niño-Southern Oscillation status remains neutral.

However, there is an increased risk of an El Niño developing this winter. This follows the sharp decline of the SOI during April, a westerly wind burst that developed in the western Pacific at the end of March, and the Bureau of Meteorology Ocean forecast model (POAMA) that continues to predict ocean temperatures consistent with an El Niño by late winter.

The strong westerly wind burst (WWB) in the second half of March initiated a Kelvin wave in the subsurface of the Pacific Ocean, which has produced some warming in the western Pacific.

During autumn and winter Kelvin Waves can be considered to be somewhat of an early indicator that there is an increased risk of an El Nino developing. They take about two months to cross to the eastern Pacific, and can trigger warming of the subsurface ocean temperatures in the Pacific as they go. However, it's too early to say just how strong this subsurface warming will be, and how far east a significant warming signal will go. Subsurface temperatures are presently cooler than average across the central to eastern Pacific, as are the surface waters.

Ocean and coupled ocean/atmosphere forecast models are used to show likely SST development out to 9 months. Of 11 models that forecast out to September, 8 indicate the continuation of a neutral SST pattern while 3 suggest the potential development of an El Nino (or warm) SST pattern.

While it is positive that more than half of these models highlight a continuing neutral SST pattern (rather than an El Nino), given current conditions (especially the recent westerly wind bursts in the central Pacific) our policy remains to recommend caution when considering the longer term outlook. This especially applies over March to June as most models fall away in their forecasting skill.

It may therefore be useful for businesses that are adversely affected by El Nino events to consider now what risk management strategies they could use if the likelihood of an event increases. More details on these models can be found at www.bom.gov.au/climate/ahead/ENSO-summary.shtml

For more information try www.longpaddock.qld.gov.au or www.dpi.qld.gov.au/climate Otherwise feel free to give me a call through the DPI call Centre on 13 25 23.